A number of power tools often require an elongated support surface for holding the workpiece being acted on by the power tool, which is significantly longer than the relatively short workpiece holding surface generally provided by the manufacturer supplied table of the power tool. Typical of such power tools are the power mitre saw, the radial arm saw with the numerous attachments such as dado cutting and router heads, the table saw and the like. For such power tools, the workpiece holding table provided by the manufacturer of the power tool typically extends only one or two feet on either side of the power tool working head member. The use of such tools, however, often require work to be performed upon a substantially elongated workpiece. For example, it is not uncommon in the carpentry trade to routinely handle and perform cutting operations upon workpieces of or in excess of 16 feet in length. In such instances, it is generally necessary to accurately support the extended workpiece along a substantial portion of its length, to ensure accurate action thereon by the power tool head.
Whenever the workpiece extends significantly beyond the edge of the work table, it becomes very difficult for the operator of the power tool to hold the workpiece in position adjacent the power tool head under the levered weight of the workpiece itself. Not only is the workpiece hard to hold in position, but the accuracy of the power tool operation upon the workpiece is generally affected. In addition, binding action of the workpiece on the power tool head can result in hazardous work conditions for the operator, particularly with powerful power tools such as radial arm or table saws.
Besides the extension's need to support the distributed weight of the workpiece, it often becomes necessary for the extension to include a vertical guide member that is accurately aligned with the vertical guide of the primary table portion of the power tool. For example, when performing such sawing operations as ripping an elongate board member, if that board is bowed along its length, unless the workpiece supporting extension includes an accurately aligned vertical guide, the resultant cut made in the board will be inaccurate, and might give rise to dangerous binding action on the saw blade. The vertical guide is particularly useful on power mitre box extensions that are generally not very wide wherein long "floppy" moldings being supported thereby would otherwise tend to slip off of the sides of the extension. In such applications, the guide also helps to maintain the pliable workpiece straight, enable accurate measurements to be made thereon. From a structural viewpoint, the guide also adds rigidity to (i.e. stiffens) the extension, reducing flexing and twisting along its length. This is particularly important to the construction of long, narrow extensions such as used with power mitre saws.
The need for power tool table extensions has been recognized in the art. The solution of providing a workable extension for handling elongate workpieces is fairly straight-forward in lumber mill operations or in permanent installations wherein the same operation is provided by the workpiece, at the same location, day after day. In such cases, it is feasible to construct a heavy-duty extension that is permanently secured to the primary table of the power tool. However, where the power tool must be used for performing a number of different operations from day to day and particularly where the power tool must be portably moved from site to site (for example in building construction projects), the problem of providing a workable, accurate, reliable and portable extension apparatus becomes more acute.
A number of such extensions have been designed in the past. However, such extensions typically do not simultaneously satisfy the combined requirements of accuracy, portability, reliability and practicality necessary for construction jobs requiring ease of mobility and rapid set-up and tear-down times. In simplest form, carpenters have been known to construct make-shift extensions at the construction site by placing a board or sheet of plywood supported by saw horses, to approximately the same height as the working surface of the primary table of the power tool. Obviously, such make-shift extensions solved few of the operator's needs or problems, and required valuable set-up time. Some manufacturers of power tools provide rigid extension wings that can be bolted to the sides of the work table to increase the support area thereof. While such devices are significantly more stable than the make-shift saw horse and board extensions, they are relatively heavy to transport, require considerable set-up and tear-down time, and due to weight restrictions, are not generally constructed in lengths sufficient to adequately support longer workpieces. Another prior art device configured for supporting long workpieces, particularly for ripping operations, used a workpiece-supporting roller mounted in a yoke, and carried by a floor stand. While useful to some extent, this device is impractical for handling warped or bowed boards, which ride poorly on the roller and sag into the area between the saw blade and the roller.
More recently, several prior art power tool table extensions, described in U.S. Pat. Nos. 4,068,551 and 4,106,381 have come much closer toward solving the practical versatility and functional use requirements for power tool extension tables. The extension structures described by these patents employ an elongate extension table mounted to the primary power saw table at their proximal ends, and supported at their distal ends by vertically adjustable legs, which allow for generally co-planar alignment of the extension table surface with the work surface of the power tool table. The extension described in U.S. Pat. No. 4,106,381, however, requires time-consuming setup for securing the extension table to the primary saw table. While the structure described in U.S. Pat. No. 4,068,551 enables faster set-up time, it uses a separate pintel fastening member which can be easily lost, mislaid or damaged during movement between construction sites. Also, if the extension is to be folded against the saw vertically as claimed, it cannot be made longer than the primary saw table is high which renders its value quite limited for supporting long boards. Therefore, while providing significant improvement over prior structures, the devices described by these patents do not provide the optimum versatility and accuracy required for many projects. Further, neither of the structures described by these patents incorporates a vertical guide member for ensuring accuracy and safety for many cutting operations.
As stated above, a portable extension member for a power tool should be of light-weight, compact and include a mechanism for rapid detachment. In addition, durability and the ability to withstand severe abuse and environmental elements also become important design factors. In practical use, such extensions are exposed to severe environmental conditions and abuse, including dirt, dust, rain, careless handling by inexperienced construction workers, and severe jostling and abuse during transport from site to site with other building materials. Obviously, the extension device would be of little use if it were readily susceptible to damage or misalignment under such typical use conditions.
While it is important that the extension be rapidly detachable from the primary power tool unit, it is also important that the extension be securely, rigidly attached to the power tool when in use. If the extension is rigidly mounted to the power tool, with no free-play (noting that most of the prior art devices have some amount of free-play), it is possible to meaningfully incorporate a ruler into the extension in a way such that measurements from the proximal end of the ruler correspond to measurements from the actual cut, or from the edge of the saw blade. Such measurement accuracy is particularly important for applications requiring extreme accuracy, as for example in performing mitre cut operations wherein small fractions of an inch difference in the cut can be important. Incorporation of one or more accurate rulers within the extension enables an operator to reliably cut materials to a specified size by simply aligning the materials with the proper measurement indicator on the ruler. In some applications, it is useful to incorporate a second ruler in the extension which is gauged to correspond identically with the proximal end of the extension. Such rulers are particularly useful for making "angled" cuts where direct measurements are inconvenient. Those extensions of the prior art that provide the convenience of rapid detachability, do not in general incorporate such rigid attachment accuracy as above described, that would enable the effective use of rulers as measuring devices as an integral part of the extension.
It is often necessary, when using such power tools as radial arm saws or power mitre box saws, to repeatedly cut a number of pieces of material to exactly the same length. For such applications, it is convenient to provide a measurement block on the extension at the proper distance from the saw blade, to which the distal end of the workpiece being cut is placed in butting engagement. Where wooden extensions have been used in the prior art, a typical way of making such a measurement block has been by simply nailing a piece of wood to the extension member at the appropriate position therealong, and by discarding the block when through with it. For extensions made of metal, and particularly whose having no vertical guides, however, it is difficult if not impossible to provide such extensions with measuring blocks. For such extensions to incorporate a measuring block, the extension must be made from a material that is strong enough to resist being deformed by the clamp or by the pressure exerted by the workpiece therethrough. Typically thin sheet metal is not sufficiently strong enough to resist such pressures. Further, if the extension is not rigily bonded to the power tool, with no free-play therebetween, usage of a measuring block can be dangerous as well as inaccurate. For example, if the extension shifts when a mitre cut is being made in a workpiece, or if the workpiece is being ripped by a saw blade, any free-play may cause the saw cerf to be pinched, resulting in jamming of the saw blade or causing dangerous "kick back"--both of which can result in injury to the operator.
The present invention overcomes many of the abovementioned shortcomings of prior art extension apparatus for use with power saws. The present invention provides a simple, reliable and versatile method and apparatus for attaching an extension to a power tool such as a saw or table. The extension apparatus incorporates an improved coupler mechanism which provides rapid attachment of the extension to the power tool, and self alignment therewith, in a manner which is repeatable with each use, and which offers no free-play between the extension and the power tool. When used with such power tools as a power mitre box or a radial arm saw, the extension apparatus can include a vertical guide, one or more intregal rulers and measuring blocks. The entire construction of the extension apparatus is sufficiently rugged so as to withstand typical use abuse and exposure to severe environmental conditions.